The art skilled man knows well the problems connected with the repeated administration of drugs. Apart from the trouble and the discomfort, mostly psychologic, which the patient can experience when he has to recollect of taking that determinate medicine three or four times a day (as it happens, for instance, with paracetamol), it must be born in mind that, from the point of view of the absorption kinetics, repeated administration is responsible of very high hematic levels of the drug which repeatedly occur in the organism of the patient, with a remarkable increase in the possibility of side effects. In the literature many methodologies are described, generically called "retard", by means of which the number of administrations of a drug can be reduced while keeping unaltered its therapeutic effectiveness during time.
Thus, for instance, slow-release tablets of indomethacin, where the active principle is coated by a film of a hydrophilic polymer and by a cellulose ether, are claimed in Japanese laid open application J 58170712, while in Japanese laid open application J 59084821, diclofenac, which is another well known antiphlogistic agent, is mixed with .beta.-cyclodestrin. In German laid open application DE 3001797, indoprofen, a good analgesic and antiinflammatory agent which has the drawback of having a short plasma half-life, is microencapsulated in a protective layer of a cellulose ether, thus obtaining a remarkable improvement of its plasma half-life. Finally, in European publications EP 0094116, EP 0094117 and EP 0094123, granules are described which have a double coating, the first made of polyvinylpyrrolidone and the second one made of acrylic polymers or by cellulose esters or by fatty or oily substances, which should allow a better release of antiphlogistic drugs either in the stomach and in the gut.
In all of these galenic formulations, however, the initial release of the active ingredient is gradual and slow, so that the therapeutic effect begins only some hours after administration. This is an evident drawback, especially in the case of drugs which contemporaneously present antiinflammatory, analgesic and antipyretic activity, where often a quick release is needed in order to obtain a prompt analgesic effect, besides the slow and regular release in order to cure the inflammation.